Carburetor



Sept. 25, 1934.

A. M. PRENTlss 1,974,585

CARBURETOR Filed Feb. 1, 1952 2 Sheets-Sheet l 5g 40 E155). 2 v

ATTORNEY.

Sept. 25, 1934. A. M. PRENTIss CARBURETOR Filed Feb. l. 1932 2Sheets-Sheet 2 IN V EN TOR.

A T TORNEY Patented Sept. 251, 1934 UNITED sf'rarasPri'rlsrr'-.oru-'icrs caaomzroa Augustin M. Prentiss, San Antonio,Tex.,- asaignor to Bendix- Aviation Corporation, South Bend, Ind., acorporation of 'Delaware Application February 1, 1932, Serial No.590,292

22 claims. (cl. zei-2s) In my patent cited, I pointed out that since.

liquids do not obey the same laws of flow as gases, it is impossible tomaintain a parity between a liquid flow and a gas fiow when caused bythe same variable effective head and the other factors influencing theflow are constant. 0n the contrary, a gas, such as air, being an elasticfluid, tends to expand and become less dense as the effective headincreases, whereas a liquid, such as gasoline, being an inelastic fluidmaintains its density and flows 'at an increasingly greater relativerate as the effective head' increases.

In my patent cited, I further pointed out that due to the inherentdifference between liquid and gas flows, any carburetor in which thegasoline` and air feeds were caused by the same ,effective head, mustnecessarily fail to maintain a iixed ratio of flows as theeffectiveghead varies. This disparity is now generally recognized asoverenrichment of the mixture-at the higher operating speeds, that is,when the intake manifold vacuum is high. To overcome this overenrichmentthe practice of bleeding air into the main fuel jet has been Widelyemployed. While this expedient, generally known as compensation, lessensthe liquid fuel flow at the higher suctions, it fails to achieve aparity of flows under varying operating heads, because it involves thesame fundamental defect it attempts to cure, that is, the differencebetween a liquid flow and a gas flow under the same varying heads. Thus,while an air bleed maybe designed to come into action, when the suctionin the carburetor reaches a certain value, dilute the mixture, and thuscorrect the overenrichment at that time, a further increase in effectivehead will again result in overenrichment as the flow of air through thebleed, following the law of gas flow, fails to keep up with theincreasing liquid fuel flow. LA

Another disadvantage of the air bleed is that it materially weakens theeffective head on the main fuel jet at low suctions, so much so, thatvarious schemes are resorted to in order to supplement the main jet feedunder low suctions. The most common of these schemes is the use of aseparate fuel and air feed for idling operation and an auxiliary fueljet usually called an economizer, arranged to come into action at lowsuctions when the throttle is wide open.

The primary object of this invention is to avoid the above diiculties byproviding a carburetor in which the volume of air iiow 'is varied inproportion as the fuel ow varies under varying effective heads, with asupplementary air flow which is regulated by the vacuum in the I mixingchamber of the carburetor.

Another object of this invention is to maintain a desired ratio betweenthe fuel supply and air supply, by the use of an air supply that,

under all operating conditions, varies directly in proportion with thefuel supply, so that a mixture of desired proportions is maintained atall times.

Still another object of this invention is to provide a carburetor inwhich the liquid fuel is fed into the mixing chamber by a positivepressure, that is, a pressure higher than atmospheric.

Stillanotherobiect of this invention is to provide a carburetor whereina portion of the air supply is fed into the mixing chamber under asuperatmospheric pressure.

A still further object of this invention is to provide a carburetor inwhich compensation for overenrichment of the. mixture is secured bycompressing a portion or all of the airsupply.

A still further object of my invention is to provide a carburetor inwhich both the liquid fuel and air supplies are subjected to asubstantially constant superatmospheric pressure'and also to a vacuumwhich varies with the demands of the engine.

A still further object of my invention is to provide a carburetorwherein the proportion of liquid fuel to air is constantly maintainedunder all operating conditionsl` at a predetermined value which may bevaried as desired. i

A still further object of my invention is to provide a carburetor havingthe above characteristics and an atomizing nozzle in which compressedair is applied to the liquid fuel column within the fuel nozzle to breakup the liquid-column before it issues from the fuel nozzle and thussecure an atomizing effect regardless of variations of specific gravityin the-liquid fuel.

Figure 1 is a central verticalcross section of my improved carburetor;

Figure 2 is a fragmentary section on an enlarged scale, along the line2-2 of Figure 1;

Figure 3 is a diagrammatic vlew,-partly in section showing the air pump,main fuel supply tank and the connections between same and the.

buretor is, for all practical purposes, sensiblyv adiabatic. Theobserved data support this view.

The general formula for liquid flow and adiabatic gas iiow, as appliedto a carburetor, may be expressed as follows:

Gi is the rate of liquid flow in pounds per second.

G2 is the rate of air flow in pounds per second.

,ui is the coeicient of efilux for liquid flow.

a2 is the coeflicient of eiliux for adiabatic gas flow.

F1 is the cross sectional area of the liquid fuel passageway of thecarburetor-generally the area of the metering restriction in the fuelpassageway.

F2 is the cross-sectional area of the main air passageway of thecarburetor in the zone of the fuel jet orificegenerally the area ofthesmallest section of the Venturi throat.

'y1 is the unit weight of the liquid fuel, in pounds per cubic foot at32 F. temperature.

'y2 is the unit weight of the air in pounds per cubic foot at normalatmospheric pressure of 32 F.

g is the acceleration of gravity.

Pn is the superior pressure causing the fluid flow, which, insuction-operated carburetors, is the atmospheric pressure outside thecarburetfxr.

Pm is the absolute pressure in the mixing chamber of the carburetor inthe zone of the fuel jet orifice.

The foregoing nomenclature and formulas are, in accordance with ChurchsMechanics of Engineerin'g, Part IY, Chapter VIII on-Kinetics of gaseousfluids.

' For convenience of reference in this specification, I shall followChurchs terminology and refer to the formula for liquid flow (Formula(l) above), as the water formula andV the'formula for air ow, (Formula(2) above), as the adiabatic formula. It will also be understood thatwhere I refer, in this specification, to the air supply to the mixingchamber of the carburetor as being fed into said chamber in accordancewith -.the law of liquid flow, I mean in accordance with the waterformula (Formula (1) above). That is to say, the total weight of airpassing into the mixing chamber, per unit of time, for any givenpressure (vacuum) in said chamber, is that found from the "water formula((1) above) for Pm equal to the pressure (vacuum) in said chamber, andnot from the adiabatic formula ((2) above) which normally governs theflow of air through a carburetor. i

It will be further understood that where I refer, in this specification,to th@ air supply to the mixing chamber being fed into the mixingchamber in accordance with the normal law of air.or gas flow, I mean inaccordance with the adiabatic gas formula (Formula (2) above) and whereI feeding liquid fuel and air under a substantially t' constantsuperatmospheric pressure to a mixing chamber through one or moreatomizing nozzles so that the liquid fuel is thoroughly atomizedregardless of variation of specific gravity. The effective head causingthe ows of liquid fuel and air is thus composed of the constantsuperatmospheric pressure mentioned plus the ordinary variable vacuum'which exists in the mixing charnber of the carburetor under variousoperating conditions. While the supply of compressed air is fed into themixing chamber under a substantially constant pressure, its rate of flowand volume is regulated in accordance with the vacuum in the mixingchamber. More particularly, the invention contemplates the use of asupplementary air supply to compensate for overenrichment of the mixturedue to the natural disparity between the liquid fuel and air fiows whencaused by a common effective head. This supplementary air supply iscontrolled by a vacuum operated valve adapted to vary the amount ofcompressed air admitted to the mixing chamber in direct proportion tothe liquid fuel admitted during the same period-of time.

Referring to the drawings, and particularly to Figure 1, the referencenumeral i denotes the body of a carburetor having an air inlet 2, aVenturi throat 3, a mixing chamber 4, and a mixture outlet controlled bya throttle valve 5. T tegral with the bottom wall of the air inlet 2 andextending to a point in the center of the throat 3, is an atomizingnozzle 6 which consists of an outer liquid fuel tube 7, a concentricinner air tube 8 and a perforated cap 9 surmounting the ends of saidtubes and adjustably attached to outer tube 7 by suitable screw threads10. By means of threads 10, the position of perforation l1 in cap 9,with respect to the end of inner tube 8, can be varied and thus regulatethe neness or coarseness of the spray issuing from nozzle 6.

Outer tube 7 communicates through a horizontal fuel passage 12 and port13 with a liquid fuel reservoir 14, in which liquid fuel enteringthrough inlet 15 is maintained at a constant level X-X by a valve 16 andfloat 17 in the usual way. Port 13.is controlled by a manuallyadjustable needle valve 18 which regulates the rate of fuel flow so thatit may be fixed at any desired ratio -with the air flow. Inner tube 8,of nozzle 6, communicates through connecting horizontal passages 19 and20, and vertical passage 21, with air supply pipe 22, through which itreceives a continuous supply of compressed air under a substantiallyconstant pressure. The rate of flow of air through passages 20 and 19,to nozzle 6, is regulated by a metering restriction 23, which, with alow effective head passes just sufficient air to thoroughly break up andato'mize the liquid fuel column which issues from tube '7 with thelowest vacuum existing in the mixing chamber under any operatingcondition. At the same time the rate of iow of liquid fuel through tube8 is controlled b y Aa superatmospheric pressure in the liquid fuelreservoir 14, which in turn, isregulated by two metering restrictions Z4and 25. Restriction 24 passes compressed air from passage 21 intoreservoir 14, and restriction 25 permits a limited portion of this airto escape from chamber 14. 'Ihe relative sizes of the two are so re- Silatmospheric.

lated, that with any desired superatmospheric pressure in passage .21, asomewhat lower superatmospheric pressure is maintained in chamber 14.The sizes of the passageways in restrictions 24 `and 25 are very smalland pass only the minimum amount of air to accomplish the foregoingresult. By the means just described, the main jet'delivers a suflicientmixture for the slowest operation of the motor, and there is no need toresort to the use of av separate idling system, as in suction operatedcarburetors where the suction on the main jet at slow speed isinsufficient to overcome the surface tension and inertia of liquid fuelcolumn in the main nozzle and withdraw liquid fuel therefrom.

Since liquid fuel and air are thus fed into the mixing chamber under apositive pressure which does not depend solely upon the vacuum in themixing chamber, there is always a suilicient mixture available for theslowest operating speeds desired, regardless of whether the throttle isin its most restricted position, as when idling, or wide open, as whenoperating at slow speed under a heavy load. For this reason nosupplementary fuel Ajets or economizers are necessary. Since liquid fueland air are fed into the mixing chamber regardless of the vacuumtherein, two other very important results are secured. First, wheneverthe throttle is moved to its most restricted position while the engineis operating, mixing chamber 4 (and even air intake chamber 2) arefilled with the mixture which issues from nozzle 6 and accumulatestherein, so that when the throttle is opened again, this additionalaccumulation of mixture is instantly available for acceleration andhence no special acceleration pump or other `device is necessary toinsure rapid and positive acceleration of the engine. Second, since theslow speed fuel feed does not depend upon the vacuum produced by thepassage of air through the Venturi throat of the carburetor, this throatcan be made relatively much larger than would otherwise be possible,Aand this in turn insures'a larger volume of air passing through thecarburetor at high speeds whereby the volumetric eilciency of the engineat such speeds is materially increased with resulting increase in powerat high speed.

Referring to Figure 3, it will be noted that fuel supply pipe 26communicates with a main fuel supply tank 27 which is provided with anair tight closure plug 28 for its filling aperture 29. Mounted upon tank27 is a compressed air dome 30 which communicates with tank 27 throughair port 31 controlled by a spring-pressed check valve 32, so arrangedthat it seats whenever the air pressure in dome 30 falls below apredetermined value (for example, two pounds per square inch) and cutsoff communication with tank 27. In this way, during operation of theengine, a predetermined minimum air pressure is always maintained in theair supply pipe 22 which connects air dome 30 with air passage 21 of thecarburetor. When the engine stops, the compressed air in passages 19 and20, pipe 22, and dome 30, escapes through nozzle 6 and that in reservoir14 escapes through orifice 25 until the air pressures therein sink to Atthe same time, since valve 32 requires a certain net pressure (of say,two pounds per square inch)Y to lift it, any compressed air up to thispressure will automatically be retained in tank 27 and this pressure issuflicient to lift the liquid fuel therein up to the carburetor bowl 14even though the carburetor be placed on a level with or above the engineintake manifold During the operation of the engine, tank 27 iscontinuously supplied with compressed air at a pressure slightlyabove-the pressurenecessary to lift valve 32, by an air pump 33, whichisgeared to -the engine by spur gears 34 and 35, and is provided with acheck valve to prevent air delivered to outlet pipe 36 'fr/om returningto the pump, and with an overflow relief valve 37 to permit the escapeinto the atmosphere of compressed air whenever the pressure in pump 33rises above a certain predetermined value. Valve 37 is adjusted by ascrew 38 which regulates the.

tension in a spring 39 which actuates the valve.

net pressure to lift valve 32, pump 33 must maintain a higher pressurein tank 27 at all times during the operation of the engine, and valve 37is set to open at this higher pressure. 0f course, it is to beunderstood that the pressures mentioned herein by way of illustrationare not to be taken as fixed values, nor even strictly relative, asobviously they may be varied within certain limits and operate thecarburetor in accordance with my invention. In this connection, it

. is also pertinent to point out that while valve 37 makes pump 33substantially a constant pressure pump, it by no means follows that thispump delivers a constant volume of air under all operating conditions.0n the contrary, as the vacuum in the mixing chamber increases, theeffective head on the air line from nozzle 6 to pump 33 likewiseincreases in proportion, since, in addition to the positive pressure inthe air line, there is also anegative pressure effective upon thedelivery end of the line which serves to augment the effective head,causing the flow of air through the line. With the increase in effectivehead increase in the flow of compressed air in accordance with the lawof adiabatic gas flow expressed by the second formula on page one ante.Since valve 37 is set so as to open only when the pressure reaches acertain predetermined value above atmospheric, the range of pumpingpressure and the volume of air delivered by the pump increases Withvacuum acting on the air line. Also since the vacuum in the mixingchamber can only increase with corresponding increase in speed of theengine, except momentarily when the throttle is suddenly, opened, andthe pump 33 is geared to the engine, the increase in volume ofcompressed air induced by the increased vacuum is automatically suppliedby the corresponding increase in the speed ofthe pump.

It is to be particularly noted that the liquid fuel is also subject tothe same range of effective heads as the air flow just described, exceptthat the constant air pressure in reservoir 14 is somewhat below that ofthe compressed air in the air line feeding nozzle 6, but this differenceis cifset by the aspirating effect on the liquid column in the fuel tube7 by the discharge of compressed air past the end of the tube 7 and outthrough orifice 11,v so that the net effective pressure on both theliquid fuel and compressed air is the same, not considering the vacuumin the mixing (pressure and vacuum) there is a corresponding i chamber.-And since this vacuum adds'equally to the effective heads of bothliquid fuel and compressed air it affects both in the same way, but notto the same extent, due to the difference in laws of liquid and gas ilowhereinbefore pointed out.

To take care of this disparity and prevent the consequent overenrichmentof the mixture as the speed of the engine increases, I have providedmeans for admitting to the mixing chamber, a supplementary air supplywhich is so regulated as to compensate for overenrichment and maintainthe mixture at any predetermined fuel air ratio desired under alloperating conditions.

In the embodiment of my invention shown in Figure l of the drawings,this means consists of the following mechanism. A cylinder 40, integralwith the bottom wall of the float reservoir 14 is divided by a wall 41into an upper chamber 42 and a lower chamber 43. Upper chamber 42 is incommunication through pipe 44, and passages 45 and- 46 with the mixingchamber 4, so that there is always substantially the same vacuum inchambers 4 and .42. Adapted'to reciprocate with an air-tight llt incharnber 42 is a piston 47 which is in the form of a cup and partiallyencloses a' helical spring 48 interposed between the piston and the topwall of chamber 42 and so arranged as to force the piston down to itslowest position when the vacuum in the mixing chamber 4 is a minimum. Asthe vacuum in the mixing chamber increases, it gradually raises piston47, against the action of spring 48, until th'e piston reaches itshighest position with its upper edge abutting the top wall of chamber42, when the vacuum in the mixing chamber is a maximum.

Adjustably attached to piston 47 by suitable screw-threads is a pistonrod 49 which passes through a liquid-tight packing gland 50 in the wall41 and is similarly attached to a cylindrical sleeve valve 51 which isadapted to reciprocate with an air-tight t in lower chamber 43. At` itsupper end chamber 43 communicates through pipe 52, passages 53 and 54and tuyres 55 with mixing vchamber 4, While at its lower end chamber 43also communicates through port 56 and passage 57 with passage 21 whichin turn connects with air pump 33 as above described. Sleeve valve 51has in its upper wall a plurality of ports 58 whose combined area equalsthe cross sectional area of each of the passages 57, 52, 53, and 54,which are-all equal, so that when valve 51 is raised so as to fullyuncover port 56, compressed air from passage 21 has an unrestricted pathto the mixing chamber'4 through the passages mentioned and tuyres 55. l

The distance between piston 47 and valve 51 is adjusted byscrew-threaded rod 49 so that when piston 47 is in its lowest position,valve 51 just closes port 56 and when piston 47 is in its highestposition, valve 5l just completely opens port 56. In order that piston47 may move freely but without sudden fluctuations in cylinder 40,chamber 42 has been placed in free communication with reservoir 14through a plurality of large ports 59 so that liquid fuel from reservoir14 freely enters and leaves chamber 42 when piston 47reciprocates-therein. The liquid fuel in chamber 42 thus steadies themovement of piston 47 and prevents fluctuations therein due to thesudden opening of the throttle. It is to be particularly noted that port56 is of peculiar shape and arrangement and herein lies the method ofregulating the amount of supplementary compressed air so that it is justthat required for compensation at all times.

From Figure .2, it will be seen that port 56 is generally of the shapeof an inverted isosceles triangle whose sides are not straight lines,but

convex curves. The total area of port 56 is approximately equal butslightly less than the crosssectional area of passage 57 so that port 56controls the iiow through passage 57 at all times. The shape of port 56is such that the area uncovered by valve 51 in any position equals thearea necessary to pass the Volume of compressed air necessary forcompensation with the vacuum existing in the mixing chamber at the time.In other Words, the uncovered area is such that with an effective head,equal to the constant superatmospheric pressure in passage 21 and thevacuum in chamber 4, the iiow of air through port 56 at any instant willbe such as to just equal the difference between the quantity of airentering chamber 4 through air inlet 2 and air tube 8, and the quantityrequired to form the desired mixture with the liquid fuel supplied tochamber 4 at that time. As the flow of air required for compensationdoes not varyv as a. simple linear function of the vacuum in the mixingchamber but at a progressively increasing rate as the vacuum increases,it is necessary that port 56 be so shaped that the area uncovered byvalve 5l will increase at the same higher rate as that required forcompensation, and the sides of port 56 are thus concave curves definingthe necessary port area for each position of the valve 51 Whose movementis controlledy by the vacuum in the mixing chamber.

Referring to Figure 4, I have shown a modification of my carburetorwherein the additional air required for compensation is taken directfrom the atmosphere instead of from the compressed air line, as inFigure 1. The only structural changes necessary are the omission of airpassage 57 and that part of cylinder 40 which covers port 56 so thatthis port opens directly into the atmosphere. Passage 21 is now reducedto the size of passage 20, as it now only supplies compressed air tonozzle 6, and pump 33 can be made correspondingly smaller. Of course,port 56 must be recalibrated and made somewhat larger as the effectivehead of air passing through it is reduced by the amount of the positivepressure in passage 57 of Figure 1. The functioning and operation ofthis modification are otherwise the same as that shown in Figure l.

In Figure 5, I have illustrated still another modification of myinvention in which the main air intake of the carburetor is completelyclosed and all of the air entering the mixing chamber is supplied underpositive pressure by the air pump. The only structural changes requiredare the following. Instead of an air intake passage 2, the body of thecarburetor extends downwardly and completely encloses the space aroundthe nozzle 6, the tuyres 55 instead of entering the mixing chamber in avertical direction near the top of the chamber, are now made almosthorizontal so as to direct the issuing currents of compressed airagainst the end of the nozzle 6, so as to baille each other and moreintimately mix with the spray issuing from nozzle 6. In thismodification the entire air supply, except the small fraction furnishedatomizing nozzle 6, passes through the compensating valve which is\structurally the same as in Figure 1 except that port 56 is recalibratedso as to pass the right amount of air for a proper mixture under alloperating conditions,

due allowance, of course, being made for the fraction of air suppliedthrough nozzle 6. Since the total air supply is here furnished by theair pump, it must be made of correspondingly-greater capacity and, ofcourse, the amount of pressure used in the air line must be increased,and to a limited extent, may be xed as desired for compressing effects.Also metering restrictions 23 and 24 must be made correspondinglysmaller.

I In operation, compressed air is supplied through pipe 22, a portion ofwhich passes through restriction 24 to maintain the fuel in the chamber14 under` superatmospheric pressure, as above explained, while anotherportion passes through restriction 23 and passages 20 and 19, to tube 8,whence it issues at 11, mingled with fuel.` Another portion of the airsupplied to the carburetor passes through port 56 and passage 53 to themixing chamber through tuyres 55, the rate of flow being varied with thesuction at 46, so thatwhen added to the quantity entering through airinlet 2 it forms a mixture of the desired richness under all operatingconditions.

the mixing chamber.

Regardless of which of the above described embodiments of my inventionare employed, the principle of operation is the same, i. e., the totalair supply to the mixing chamber varies with the pressure (vacuum)insaid chamber in accordance with the water formula (Formula 1) and notin accordance with the adiabatic formula (Formula v2). This result issecured as follows: The carburetor in the form shown in Figure l, isoperated first as a simple suction-feed carburetor,

with all supplementary air through port 56 shut off, under various loadsand speeds from minimum to maximum. The pressures (vacuums) in mixingchamber 4 are ascertained by a manometer connected thereto and thecorresponding flows (by weight) of liquid fuel and air are measured byflow meters. Under'- these conditions the flow of air for each degree ofpressure (vacuum) in the mixing chamber is determined and is found tocorrespond very closely with the adiabatic formula cited ante.Similarly, the flow of liquid fuel is determined for each degree ofpressure (vacuum) in the mixing chamber and is found to correspond withthe water formula cited ante. The deficiency in the air flow for eachdegree of mixing chamber pressure (vacuum) is then found by subtractingthe air flow, determined as just described, from the corresponding fuelflow multiplied by the desired mixture ratio (as 16:1). The valve 51 andIport 56 are then designed to pass an amount of supplementary air equalto the deficiency in the main air supply, as thus determined, for eachdegree of pressure .(vacuum) in Since the valve 51 is responsive to thevacuum in the mixing chamber, and moves indirect proportion to theintensity of said vacuum, the correct amount of supplementary air to bepassed into the mixing chamber is a function of the area of port 56 foreach position of valve, and port 56 is shaped accordingly. After theforegoing data is determined, if the embodiment of my invention shown inFigure l is to be used, the port 56 is designedto pass the supplementaryair supply, determined as above, under a head, consisting of theconstant superatmospheric air pressure supplied by pump 33, plus thevariable vacuum in mixing chamber 4. If the form shown in Figure 4 is tobe used, port 56 is designed to pass the same supplementary air supplyunder a head consisting of the variable vacuum -in mixing chamber 4above, while if the form shown in Figure 5 is used, port 56 is designedto pass a total air supply equal .tothe entire required air supply,determined as above,

under a head consisting of the constant super`V atmospheric pressure ofpump 33 plus the variable vacuum in chamber 4. j

From what has been said above, it is seen that, irrespective of theparticular embodiment of my invention employed, the total air supplyflowing into the mixing chamber for any particular degree of vacuumtherein corresponds to that shown by the water formula and not thatshown by the adiabatic formula. Since the liquid fuel also fiowsaccording to the water formula it follows that the ratio between the.air supply and liquid fuel supply can be held constant under alloperating conditions, or can be varied'as desired by suitably changingthe shape of port 56.

While the air entering the carburetor through air inlet 2 and thatentering through passageway 23 and nozzle 6, separately considered, flowaccording to the natural law of air flow (i. e. adiabatic fcrmula) theamount of supplementary air entering through nozzle 6 is so controlledwith reference to the vacuum in the mixing chamber, that the totalamount of air entering the mixing chamber per unit of time, (i. e., therate of total air flow) is equal to that shown by the water formula foreach corresponding degree of vacuum in the mixing chamber. Hence, inthis specification where I speak of so regulating the air supply as tomake it ow in accordance with the law of liquid ow, it will beunderstood that I mean theV total amount of air entering the mixingchamber, per unit of time, is that corresponding to the water formula,and n'ot the adiabatic formula, for each corresponding degree of vacuumin the mixing chamber.

While I have shown and described the preferred embodiment of myinvention, I desire it to be understood that I do not limit myself tothe constructional details shown by way of illustration as these may bemodifed in combination and arrangement by those skilled in the artwithout departing from the spirit of my invention or exceeding the scopeof the appended claims.

I claim:

1. In a carburetor, ,a mixing chamber, an atomizing nozzle, an airsupply and a liquid fuel supply to said nozzle, both under asuperatmospheric pressure, andv a vacuum-controlled compressed airsupply to said mixing chamber.

2. In a carburetor, a mixing chamber, an atomizing nozzle in saidchamber, an air supply and a liquid fuel supply to said nozzle, bothunder a superatmospheric pressure, an additional air supply to saidmixing chamber, means for compressing said additional air supply, andmeans for admitting said compressed air to said mixing chamber so as tomake the total air supplied to said chamber always bear a predeterminedratio to said liquid fuel supply.

3. In a carburetor, a venturi, a fuel nozzle, a mixing chamber, airinlets anterior and posterior to the fuel nozzle, and means forsupplying air to the posterior inlet at a superatmospheric pressurevarying with the pressure in the mixing chamber. f

` and a valve in said conduit responsive to pressures in said mixingchamber.

5. In a carburetor, a venturi, a 'fuel nozzle, a mixing chamber, an airinlet posterior to the fuel nozzle, and means for supplying air to saidair inlet comprising a source of superatmospheric pressure air, aconduit leading from said source to said mixing chamber, a valvecontrolling said conduit, and control means for said ,valve responsiveto pressures existing in saidmixing chamber.

6. In a carburetor, a mixing chamber, an air supply at atmosphericpressure, a compressed air supply, and a liquid fuel supply thereto, andautomatic pressure-responsive means for regulating the compressed airsupply so as to make the total air supplied vary in accordance with thelaw of liquid flow, and thereby always bear a predetermined ratio tosaid liquid fuel supply.

7. In a carburetor, a mixing chamber, an air supply and a liquid fuelsupply thereto, means for compressing a portion of the air supply andmeans for admitting said portion to said mixing chamber so as to makethe total air supply vary in accordance with the law of liquid flow,whereby the total air supply always bears a predetermined ratio to saidliquid fuelsupply.

8. In a carburetor, a mixing chamber, means for supplying theretoliquidA fuel and air, both under superatmospheric pressures, and meansfor regulating the air supply so as to make it vary in accordance withthe law of liquid fiow and thereby always bear a predetermined ratio tosaid liquid fuel supply.

9. In a carburetor, a mixing chamber, an air supply at atmosphericpressure and a liquid fuel supply thereto, and automatic pressure,responsive means for feeding compressed air thereto at such a rate thatthe total air supply varies in accordance .with the law of liquid flow,whereby the total air supply always bears a predetermined ratio to theliquid fuel supply.

10. In a carburetor, a mixing chamber, means for feeding liquid fuelthereto and means comprising a variable vacuum and a constantsuperatmospheric pressure for feeding to said chamber air at a ratewhich varies in accordance with the law of liquid flow.

11. In a carburetor, a mixing chamber, means for feeding liquid fuelthereto, means fr feeding air thereto comprising the vacuum within saidchamber and a superatmospheric pressure such that the total air supplyvaries in accordance with the law of liquid iiow, whereby a constantratio is maintained between the liquid fuel and air in said chamber.

12. In a carburetor, a. mixing chamber, an atomizing nozzle in saidchamber, an air supply and a liquid fuel supply to said nozzle, bothunder superatmospheric pressures, a supplementary air supply to saidchamber, and means for admitting said additional air supply to saidchamber at such a variable rate that the total air supplied to saidchamber always bears a predetermined ratio to said liquid fuel supply.

13. In acarburetor, a mixing chamber, means for supplying thereto liquidfuel and air each under an effective head which comprises a constantsuperatmospheric pressure and a variable vacuum, and means for admittingsaid air to said chamber at a rate which varies in accordance with thelaw of liquid flow, whereby a constant ratio is maintained between theliquid fuel and air in said chamber.

14. In a carburetor, a mixing chamber, an

atmospheric air supply to said chamber, an atomizing nozzle in saidchamber and comprising an air tube and a liquid fuel tube, means forsupplying air and liquid fuel to said tubes respectively, each under aneffective head consisting of a constant superatmospheric pressure plus avariable vacuum, such that the total air supply varies in accordancewith the law of liquid flow.

15. In a carburetor, a mixing chamber, means for supplying theretoliquid fuel and air, each under a superatmospheric pressure, andvacuumactuated means for regulating the air supply so as to make italways bear a predetermined ratio to said liquid fuel supply.

16. In a carburetor, a mixing chamber, means for supplying theretoliquid fuel and air, each under a constant superatmospheric pressure,and means for regulating the air supply so as to make it vary inaccordance with the law of liquid flow, and thereby always bear apredetermined ratio to said liquid fuel supply.

' 17. In a carburetor, a mixing chamber, an air supply at atmosphericpressure, a compressed air supply, and a liquid fuel supply thereto, andmeans for admitting said compressed air supply to said chamber at alrateequal to the difference between the rate of said atmospheric air supplyflowing in accordance with the law of gas flow, and a predeterminedmultiple of said liquid fuel supply flowing in accordance with the lawof liquid flow, whereby the total air supply always bears apredetermined ratio to said liquid fuel supply.

18. In a carburetor, a mixing chamber, an air supply at atmosphericpressure, a compressed air supply under constant pressure, and a liquidfuel supply thereto, and means for varying the flow of compressed air sothat the total air supply varies in accordance with the law of liquidflow, whereby a predetermined ratio is always maintained between thetotal air supply and the liquid fuel supply.

19. In a carburetor, a mixing chamber, an air supply thereto atatmospheric pressure, a compressed supply and a liquid fuel supplythereto under constant superatmospheric pressures, and meansfor varyingthe ows of both air supplies so that the total air supply varies inaccordance with the law of liquid flow, whereby a predetermined ratio isalways maintained between the total air supply and the liquid fuelsupply.

20. In a carburetor, a mixing chamber, an air lsupply under atmosphericpressure and a liquid fuel supply thereto, means including a passagewayfor supplying compressed air to said chamber, and means for regulatingsaid compressed air supply by varying the size of said passageway,whereby the total air supply to said chamber varies in accordance withthe law of liquid flow.

2l. In a carburetor, a mixing. chamber, means yfor supplying theretoliquid fuel and air each under a superatmospheric pressure, and meansincluding a vacuum-actuated valve, for regulating said air supply so asto make it always bear a predetermined ratio to said liquid fuel supply.22. In a carburetor, a mixing chamber, means for supplying theretoliquid fuel and air each under a superatmospheric pressure, and meansincluding a valve, actuated by the pressure in said chamber, forregulating said air supply so as to make it always bear a predeterminedratio to said liquid fuel supply.

' AUGUSTIN M. PRENTISS.

